FIG. 1 is a diagram for a heterogeneous network wireless communication system 100 including a macro base station and a micro base station. In this disclosure, a terminology named a heterogeneous network means a network having a macro base station 110 and micro base stations 121 and 122 coexist therein despite using the same RAT (radio access technology).
The macro base station 110 has a wide coverage and a high transmission power and means a general base station in a wireless communication system. The macro base station 110 may be called a macro cell.
Each of the micro base stations 121 and 122 may be called such a name as a micro cell, a pico cell, a femto cell, a home eNB (HeNB), a relay and the like. Each of the micro base stations 121 and 122 is a small-scale version of the macro base station 110 and can independently operate by performing most of the functions of the macro base station 110. And, each of the micro base stations 121 and 122 may include a base station of an overlay type that is installed within an area covered by the macro base station. Moreover, each of the micro base stations 121 and 122 may include a base station of a non-overlay type that can be installed in a radio shadow area not covered by the macro base station. Each of the micro base stations 121 and 122 can accommodate a smaller number of user equipments with a coverage and transmission power smaller than those of the macro base station 110.
One user equipment 131 may be directly served by the macro base station 110 [hereinafter such a user equipment shall be called a macro user equipment (macro-UE)]. Another user equipment 132 may be served by the micro base station 122 [hereinafter such a user equipment shall be called a micro user equipment (micro-UE)]. Occasionally, the user equipment 132 existing within the coverage of the micro base station 122 may be served by the macro base station 110.
Micro base stations may be classified into two kinds of types depending on whether restriction is put on an access by a user equipment. A firstfirst type corresponds to a CSG (closed subscriber group) micro base station. And, a second type corresponds to an OSC (open subscriber group) micro base station. The CSG micro base station can serve specific access-granted user equipments only, while the OSG micro base station can serve all user equipments without separate access restriction.
Meanwhile, PDCCH (physical downlink control channel) is the channel that carries control information provided to a user equipment by a base station. Information indicating that PDCCH is carried on a prescribed number of time units (e.g., OFDM (orthogonal frequency division multiplexing) symbol(s), etc.) in a downlink subframe can be provided to a user equipment by a base station through PCFICH (physical control format indicator channel).